The present invention relates to electrical switches, and more particularly, to switches operated by centrifugal forces imparted through the rotation thereof.
It is known to provide electric motors with starter windings in addition to the normal run windings. The starter windings, as the name implies, are used upon startup of the motor to achieve higher levels of starting torque. As the motor reaches operating speeds, the circuit to the starter windings is interrupted. Various switching devices are known for interrupting the starter winding circuits.
Devices can be attached to the motor shaft or rotor, and include components moved by centrifugal force when the motor achieves a desired operating speed. Movement of the components by centrifugal force is used to operate circuit control switches. Such centrifugal switches can have wide application and use, including the control of starter winding circuitry.
In some centrifugal switches, metallic contact slip rings and brushes run in substantially continuous contact during motor operation, which can result in excessive wear to the parts. Magnetically attracted contacts also have been used, to keep the circuit closed. As the motor achieves the desired operating speed, centrifugal forces are used to overcome the magnetic attraction and open the starter winding circuit. Accumulation of dirt and grime on the magnetic contacts adversely affects this type of switch by affecting the strength of the attractive force. Other centrifugal switches are complex in construction, with several linkages and mechanism. Complex switches can be expensive to manufacture, and can be prone to failures.
The target speed of rotation at which the starter windings are deactivated can vary significantly from one motor to another. It is desirable to have a more or less standardized basic structure for a centrifugal operated switch, which can be customized for specific uses. Many structures known heretofore for centrifugal switches are customized to specific motor applications and target speeds, requiring substantial redesign for use on another motor and for another target speed. This requires manufacturers to stock completely different switches for the different uses to which the switches will be put.
The present invention is directed to overcoming one or more of the problems set forth above.
The present invention provides a centrifugal operated switch mechanism that is reliable and customizable for specific applications.
In one aspect thereof, the present invention provides a centrifugal switch with a first electrical terminal, a second electrical terminal, and an electrical contactor for establishing an electric circuit connection between the terminals. The contactor has an end movable relative to one of the terminals. A spindle is mounted for rotation. A plunger engages the contactor, and at least one swing arm is rotated by the spindle and pivotally mounted for movement by centrifugal force. The swing arm is connected to the plunger for movement thereof upon movement of the swing arm.
In another aspect thereof, the invention provides a centrifugally operated switch, with a housing; a spindle vertically mounted in the housing for rotation and having an upper end in the housing; and a plunger at the upper end of the spindle. The plunger is configured for vertical movement in the housing. Opposed swing arms are connected to the spindle for rotation by the spindle. The swing arms each are connected about a substantially horizontal pivot and have a lever below the pivot. The lever has a distal end engaging the plunger for pushing downwardly on the plunger as a rotational speed of the spindle increases. An electrically conductive contactor extends between first and second terminals, the contactor being connected to the plunger and having an end movable relative to one of the terminals upon vertical movement of the plunger.
In yet another aspect thereof, the present invention provides a method for operating a centrifugal switch, having steps of providing a housing with electrical terminals therein, a movable contactor between the terminals, a spring engaged with the contactor under tension, a spindle mounted for rotation in the housing and a plunger disposed between the spindle and the contactor; providing swing arms rotated by the spindle and responsive to changes in centrifugal force to cause movement of the plunger; moving the plunger by changing centrifugal force on the swing arms; deflecting a portion of the spring to urge the contactor into engagement with one of the terminals; and removing deflection of the spring to urge the contactor away from the one of the terminals.
In still another aspect thereof, the invention provides a centrifugally operated switch with a housing and a spindle vertically mounted in the housing for rotation. A plunger at an upper end of the spindle is configured for vertical movement in the housing. A first spring biases the plunger upwardly. Opposed swing arms are connected to the spindle, for rotation by the spindle. The swing arms are each connected about a substantially horizontal pivot and have a lever below the pivot. The levers have distal ends engaging the plunger for pushing downwardly on the plunger as a rotational speed of the spindle increases. First and second spaced electrical terminals are provided in the housing, with an electrically conductive contactor having a first end engaged with the first terminal and a second end movable between contacting and non-contacting position with the second terminal. A second spring is disposed under tension between the first terminal and the contactor. The second spring is adapted and arranged to urge the second end of the contactor away from the second terminal in a non-deflected position of the second spring, and to urge the second end of the contactor into engagement with the second terminal in a deflected position of the second spring. A coupling engages a portion of the second spring and the plunger, to transfer movement of the plunger to cause deflection of the second spring.
An advantage of the present invention is providing a centrifugal switch useful for switching the starter windings of a motor, and which can be adjusted or modified easily and quickly for use at different target speeds for switch activation, thereby reducing the number of parts required for motor manufacturers to stock.
Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description, claims and drawings in which like numerals are used to designate like features.